I would imagine it could only be useful for 30 minutes before the cell would be unusable. Arent solar cells just P-N junctions where if it is really thin it would just run out of holes to fill?
Edit: why am I being downvoted? To my limited understanding from my electrochemistry courses from 10 years ago, photovoltaics depend on the density. Theres only a limited amount of free electrons and only a limited number of free holes. The thinner the material the less likely an electron hole can get filled with whatever N-doped semiconductor used.